A gas turbine engine is typical of the type of machinery in which the invention described herein may be advantageously employed. It is known that a gas turbine engine conventionally comprises a compressor for compressing inlet air to an increased pressure for delivery to a combustion chamber. A mixture of fuel and the increased pressure air is burned in the combustion chamber to generate a high temperature gaseous flow-stream from which work is extracted by a plurality of rotatable turbine blades within a turbine.
In an effort to reduce the specific fuel consumption of gas turbine engines, there has been a move to increase the turbine efficiency by decreasing the clearance between the turbine blade tips and the non-rotating blade track. In designing a gas turbine engine with tighter blade tip clearances, designers must account for transient conditions that many gas turbine engine experiences during operation. During acceleration of the gas turbine engine, the rotor carrying the turbine blades experiences mechanical growth in a radial direction faster than the blade track, thereby allowing the potential for mechanical contact between the blade tips and the blade track. During deceleration of the gas turbine engine, the blade tracks exhibit mechanical shrinkage in the radial direction more quickly than the rotor, thereby allowing the potential for mechanical contact between the blade tips and the blade tracks.
The present invention provides a novel and non-obvious method and apparatus for controlling the blade tip clearance in a gas turbine engine.